A diaphragm-type carburettor comprises a main body portion defining a carburettor mixing passage or bore having an air intake side and an engine outlet side, fuel pump means, a throttle shutter mounted within the carburettor mixing passage between the air intake side and the engine outlet side, a throttle shaft for controlling the throttle shutter, and a metering chamber for supplying fuel from the fuel pump means into the carburettor mixing passage via a high-speed adjusting screw and a low speed/idle adjusting screw.
In such a carburettor the volume of fuel delivered to engine is adjustable, for low speed operation via low speed/idle adjustment screw and for high-speed operation via the high-speed adjustment screw.
Adjustment is factory set by the engine manufacturer to give the desired engine performance/air fuel ratios.
With such a system, adjustment can be made within a broad band from no fuel flow, when the adjustment needle is screwed fully in (i.e. the needle tip closes the orifice) to fully open, when the needle tip is fully out of the orifice. In this case the orifice diameter controls the maximum volume of fuel flow. This system allows the engine to be set to run on a very lean or very rich fuel fixture. More often the factory setting is re-adjusted by the end user because of acceleration problems due to the carburettor supplying insufficient fuel on acceleration and or altitude conditions where by the engine runs lean or rich due to the altitude. This arises from the inertia of moving components and machining in the carburettor, as well as high temperatures, pressures and vibration from the engine to which the carburettor is fitted. If sufficient fuel is supplied for acceleration, this can lead to an over supply at other times, causing engine performance problems in start-up, warm-up, lower and part throttle positions.
It is an object of the present invention to provide an electronic control system for a carburettor in which the above problem can be avoided.
This invention addresses the above problem by providing a fuel control system for a carburettor which has the ability to supply the correct quantity of fuel when required throughout the full range of operation or may be set to cover only a particular section of the full range of operation, primarily allowing the engine to have stable operation.